Magneto-optical recording media have been in practical use as rewritable optical recording media. Information is recorded on such a magneto-optical recording medium by converging semiconductor laser light on the magneto-optical recording medium and aligning the magnetization direction in a portion showing a rise in temperature with the direction of an external recording magnetic field applied. On the other hand, information is read out from the recording medium by converging the same semiconductor laser light on the recording medium after decreasing the power of the semiconductor laser light and detecting the polarized state of reflected light.
In order to decrease a recording magnetic field required for recording, a magneto-optical recording medium including a recording layer made of TbFeCo and a magnetic layer made of Co which achieve exchange coupling with each other was proposed in the Magneto-optical Recording International Symposium 1994 (28-F-03). Moreover, a magneto-optical recording medium including a recording layer made of TbFeCo and a magnetic layer made of GdFeCo which achieve exchange coupling with each other was proposed in the International Symposium on Optical Memory 1995 (Fr-D5). In these magneto-optical recording media, a magnetic layer is exchange-coupled with a recording layer. It is therefore possible to reverse the magnetization of the recording layer exchange-coupled with the magnetic layer by reversing the magnetization of the magnetic layer in recording. If a material whose magnetization is reversed at a lower magnetic field strength than that for the recording layer is used for the magnetic layer like the above-mentioned examples, it is possible to achieve recording at a lower magnetic field strength.
By the way, if the recording bit diameter as a recording magnetic domain and the recording bit interval become smaller than the beam diameter of a light beam which is emitted by the semiconductor laser and converged on the magneto-optical recording medium, deterioration of the readout characteristics occurs for the reason below. When the light beam is converged on a target recording bit, an adjacent recording bit enters into the beam diameter, and thus individual recording bits cannot be read out separately.
In order to solve such a drawback, Japanese Publication for Unexamined Patent Application No. 150418/1994 (Tokukaihei 6-150418) proposes a magnetically induced super resolution magneto-optical recording medium including a readout layer which is in an in-plane magnetization state at room temperature and changes into a perpendicular magnetization state with a rise in temperature, and a non-magnetic intermediate layer between the readout layer and a recording layer which achieves magnetostatic coupling with the readout layer.
In this structure, information recorded in a recording magnetic domain in the in-plane magnetization state is masked. Therefore, even when an adjacent recording bit enters into the diameter of the light beam converged on the magneto-optical recording medium, it is possible to separately read out individual recording bits, thereby achieving magnetically induced super resolution readout.
Thus, the recording magnetic field can be certainly decreased by achieving exchange coupling between the recording layer and the magnetic layer like the above-mentioned conventional examples. However, in order to meet recent high-speed, more compact, less power consuming recording and reading apparatuses, a further decrease in the recording magnetic field is required for the magneto-optical recording media and magnetically induced super resolution magneto-optical recording media.